Storage libraries provide large capacity secondary storage to modern computing requirements. Such storage libraries typically employ robotic control mechanisms used by a host computer to physically manage tape media cartridges. A plurality of tape cartridges are stored within a storage library. Each tape cartridge is in a particular slot in the storage library. Each slot is identifiable by its physical position in the storage library. Each tape cartridge is typically uniquely identified by a machine readable label. The storage library maintains inventory information to associate a particular tape cartridge with a particular slot in the storage library. Responsive to a host computer request, a robotic mechanism physically retrieves an appropriate tape cartridge from its associated slot in the storage library, moves the tape cartridge to an appropriate read/write device for processing, and inserts the tape cartridge into the device.
The robotic mechanism typically includes a hand or gripper mechanism positioned on a movable arm. To retrieve a tape cartridge, the arm moves to position the gripper near the slot holding the desired tape cartridge. The gripper then extends and grips the tape cartridge and retracts to take the tape cartridge out of the slot. The arm with the hand gripping the tape cartridge moves to the device and the hand then extends and inserts the tape cartridge into the device. Conversely, when the use of the tape cartridge is complete, the robotic mechanism retrieves the tape cartridge from the read/write device, moves the tape cartridge adjacent its associated slot according to the inventory maintained by the storage library, and inserts the tape cartridge into the storage slot of the storage library ready for future use in response to another host computer request.
A problem with prior designs which contributed to their relatively higher complexity and resultant higher costs relates to the multiplicity and complexity of various sensing mechanisms used to sense several parameters of the operating storage library. A first sensing mechanism determines if there are any obstructions in the path of movement of the gripper which could damage the gripper, the obstruction, or the tape cartridges. A second sensing mechanism independently senses the presence or absence of a tape cartridge in a storage slot. A third sensing mechanism independently reads machine readable labels on tape cartridges (bar code labels or other optically encoded labels). A fourth sensing mechanism independently distinguishes between labeled and unlabeled tape cartridges. A fifth sensing mechanism independently calibrates the position of the robotic mechanism.
What is needed is a simpler, lower cost apparatus to sense the presence of robotic mechanism path obstructions, to sense the presence and absence of tape cartridges in their associated slots, to read the labels of the tape cartridges, to distinguish between labeled and unlabeled tape cartridges, and to calibrate the position of the robotic mechanism.